This invention relates broadly to methods and apparatus for uniformly establishing viewable characteristics, such as brightness and contrast, of television receivers. In particular, it relates to means for automatically "setting up" color television receivers in a factory environment.
As is readily obvious to most television viewers, it is difficult to obtain similar renditions of like program material on different receivers, even though the receivers are produced by the same manufacturer. With color receivers the differences are more pronounced in that the eye is extremely sensitive to chromatic differences in a side-by-side viewing situation. The problem stems mainly from the fact that "set up" of receiver characteristics, such as brightness, contrast, color saturation and tint involves highly subjective judgments which must be made fairly rapidly. To alleviate this condition, most manufacturers utilize some form of instrumentation to assist skilled technicians in factory adjustment of television receivers.
As is well known, color television receivers include picture tubes having viewing screens comprising a plurality of individual phosphor deposits which, when excited by electrons, emit light of individually different colors. Conventionally, red-light emitting, blue-light emitting and green-light emitting phosphors are used. Such tubes also include some type of parallax barrier or shadow mask between the electron beam gun assembly and the phosphor deposits for shadowing the different colored-light emitting phosphor deposits from electrons emitted by other than their corresponding electron guns.
Some known ways of setting up color receivers in the factory utilize photocells for developing electrical signals in accordance with the light characteristics produced by a test signal pattern displayed on the reciever picture tube, for operating electrical meters or "go", "no-go" lights which the operator notes as he adjusts the various receiver adjustable control elements. Unfortunately, the viewable characteristics are not independent of each other and the corresponding receiver control elements are thus interactive. The operator, therefore, must move from control to control while noting the effect of adjustments on the meters or lights in an attempt to arrive at the correct settings. For example, the brightness of the displayed image will be affected by the contrast setting and vice versa as will color saturation and tint. Further, the operator is generally trying to obtain a maximum reading and it is difficult to determine because the response is somewhat broad. Consequently, it is a difficult operation to adjust these four characteristics utilizing techniques of the prior art.
A further problem is introduced by the parallax barrier (shadow mask) in color picture tubes which intercepts a major portion of the electron beams directed toward the screen. The energy dissipated at the mask causes it to experience thermal changes, not only affecting its position relative to the screen, but also changing the size of its apertures. Also, to minimize the effect of adjustment errors, it is desirable to produce high brightness and contrast levels in the test pattern which causes small areas of the shadow mask to absorb intense electron beam energy. The local heating of these mask areas results in receiver settings which are abnormal. Thus the technician tends to make adjustments as rapidly as possible to minimize the influence of these temperature effects on the meter readings.
In the last few years, many color television receiver manufacturers have incorporated a "preset" or "factory adjustment" position to enable the viewer to switch the receiver to optimum factory setup conditions. These preset factory adjustments may be established by an alternate set of viewer-inaccessible control elements which are rendered operational by a viewer-accessible switch. Some other arrangements have a single set of operating control elements and the preset condition is established by switching range-restricting networks into circuit with the control elements.
A common cause of complaint on the part of new color set owners is that of improper receiver setup for which a service call is normally required. Without some objective criteria againt which the receiver factory setup may be judged, it is all but impossible to reduce the number of such service calls sinve the uniformity of the product leaving the factory cannot be sufficiently controlled. It is, therefore, very desirable to have some method and apparatus available, in the factory, for establishing the color characteristics of a receiver in an objective manner and thus insuring a high degree of uniformity in setup.